Scissortail Chromis, Chromis atrilobata
The Scissortail Chromis, Chromis atrilobata, whose common Spanish name is castañeta cola de tijera, is a species in the Damselfish or Pomacentridae Family, known collectively as castañetas and jaquetas in Mexico. Globally, there are eighty-four species in the genus Chromis, eight of which are found in Mexican waters, five in the Atlantic and three in the Pacific.
The Scissortail Chromises have narrow oval fusiform compressed bodies with a depth that is 36 to 40% of standard length, thus similar in nature to freshwater bluegills. They are metallic silvery gray in color with dark reddish brown tinges. Most fish have a prominent white spot just below the end of their dorsal fin base. Their caudal fin is deeply forked and each fin lobe is narrow and intensely black with sharp tips, thus resembling a pair of scissors (after which they are named). Their pectoral fin base is also very black. Their head has a small protrusible mouth that opens in the front with two rows of teeth. They have two anal spines and 10 to 12 rays, a single continuous dorsal fin with 12 spines and 12 or 13 rays, and 20 to 23 gill rakers on their lower arch. Their lateral line is incomplete and ends under the edge of their dorsal fin base. Their body is covered with large rough scales.
The Scissortail Chromis are a non-migratory species normally found in shallow water in large aggregations around rocky reefs, but they are also found at depths up to 260 feet. They reach a maximum length of 13.4 cm (5.3 inches). They are diurnal feeders consuming primarily algae, plankton, and benthic invertebrates. Reproduction is oviparous with pairing of individuals; eggs are distributed demersal and adhere to the substrate due to their stickiness.
In Mexican waters the Scissortail Chromis are found in all waters of the Pacific with the exception that they are absent from Guerrero Negro northward along the central and northwest coasts of Baja.
The Scissortail Chromis is very easy to identify, however, it is most likely confused with the Silverstripe Chromis, Chromis alta (deep body lacking caudal fin; sharp dark lobes; white spot at base of dorsal fin).
The Scissortail Chromises are small and rare and of limited interest to most. They are classic nibblers, thus difficult to catch by hook and line.
Silverstripe Chromis, Chromis atrilobata. Fish caught from coastal waters off Puerto Los Cabos, Baja California Sur, October 2008. Length: 14.0 cm (5.5 inches). Provided by regurgitation by a Flag Cabrilla.
Scissortail Chromis, Chromis atrilobata. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, December 2010. Length: 8.9 cm (3.5 inches). Note that this fish lacks the prominent white spot at the rear base of the dorsal fin.